1. Field of the Invention
The present invention relates to a supply pump for supplying diesel fuel. In particular, the present invention is directed to an improved embodiment of the slide bearing arrangement for bearing the drive shaft in the housing of the supply pump.
2. Description of the Prior Art
One generic supply pump for supplying diesel fuel is known from German Published Patent Application DE 101 38 362 A1. The supply pump serves to supply diesel fuel to a so-called common rail fuel injection system. The so-called common rail forms a high-pressure reservoir, whose high pressure is maintained by means of the supply pump. The supply pump has a housing, with a drive shaft received in it that is supported rotatably about a drive shaft axis by means of two slide bearing arrangements. The slide bearing arrangement is formed by a bearing bore and by a bearing shaft portion that extends through the bearing bore. The bearing shaft portion forms a part of the drive shaft, and the bearing arrangements are preferably disposed adjacent to a cam portion, over which a roller rolls, and thus is operatively connected to a valve combination. The slide bearing arrangement includes one bearing bush each, in which the bearing bore is embodied.
A further embodiment of a supply pump of this generic type is disclosed in German Published Patent Disclosure DE 199 13 804 A1. The supply pump serves to supply fuel to a high-pressure reservoir for an internal combustion engine, and the supply pump is embodied with two pump chambers that are in line with one another. The valve combinations in this version are actuated via two cam drive mechanisms, disposed adjacent one another on a drive shaft, and the cam drive mechanisms are received on the drive shaft between two slide bearing arrangements. Thus an advantageous load situation develops between the bearing arrangements.
With a view to generating the reciprocation of the reciprocating element extending into the valve combination, the supply pump can be embodied with a cam drive mechanism or with an eccentric drive mechanism. However, in both types of such supply pumps, the problem arises that because of the very high supply pressures, strong forces act on the drive shaft and have to be absorbed by the slide bearing arrangements. These forces are introduced into the drive shaft via the pressure rollers onto the cam portions and are due to the respective valve combinations. In addition, major shear forces can be introduced into the drive shaft, caused by units that are likewise driven via the drive shafts. The drive shaft extends out of the housing of the supply pump in at least one direction, and it receives at least one transmission mechanism for transmitting power by means of a traction mechanism, toothing, or the like. If, for the sake of power throughput, additional units are driven via the drive shaft of the supply pump, then considerable forces may be introduced into the drive shaft and must likewise be absorbed by the respective slide bearing arrangement. Resultant sagging of the drive shaft leads to edge supports in the bearing edges, which cause very strong edge pressures between the bearing shaft portion and the bearing bore. The high values of the bearing pressures can have the effect that a load-bearing film of lubricant between the bearing bore and the bearing shaft portion can no longer develop, which can lead to considerable wear and premature failure of the supply pump. Conventional bearing arrangements in the prior art have a cylindrical embodiment, so that the bearing shaft portion and the bearing bore each form a concentric cylindrical portion.
Slide bearings have a typical bearing clearance, which forms as a difference in diameter in the radial direction between the bearing shaft portion and the bearing bore. A bearing clearance of this kind is provided in order to form hydrodynamic lubrication by means of a lubricant, such as lubricating grease or lubricating oil. If the drive shaft tilts slightly, either from a skewed position, that is, a skewed course through the two slide bearing arrangements, or from sagging of the drive shaft, the result is an incorrect position geometrically; that is, the alignment of the bearing bore no longer matches the alignment of the bearing shaft portion.